All Results

The e ective neutrino mass of neutrinoless double-beta decays:how possible to fall into a well

Zhi-zhong Xing; Zhen-hua ZhaoSubjects: Physics >> General Physics: Statistical and Quantum Mechanics, Quantum Information, etc.

The neutrinoless double-beta (0ν2β) decay is currently the only feasible process in particle and nuclear physics to probe whether massive neutrinos are the Majorana fermions. If they are of the Majorana nature and have a normal mass ordering, the e?ective neutrino mass term mee of a 0ν2β decay may su?er signi?cant cancellations among its three components and thus sink into a decline,resulting in a “well” in the three-dimensional graph of |mee| against the smallest neutrino mass m1 and the relevant Majorana phase ρ. We present a new and complete analytical understanding of the ?ne issues inside such a well, and identify a novel threshold of |mee| in terms ofthe neutrino masses and ?avor mixing angles: |mee|? = m3 sin2 θ13 in connection with tan θ12 = m1/m2 and ρ = π. This threshold point, which links the local minimum and maximum of |mee|, can be used to signify observability or sensitivity of the future 0ν2β-decay experiments. Given current neutrino oscillation data, the possibility of |mee| < |mee|? is found to be very small. |

A review of μ-τ flavor symmetry in neutrino physics

Zhi-zhong Xing; Zhen-hua Zhao1Subjects: Physics >> Nuclear Physics

Behind the observed pattern of lepton flavor mixing is a partial or approximate mu-tau flavor symmetry --- a milestone on our road to the true origin of neutrino masses and flavor structures. In this review article we first describe the features of mu-tau permutation and reflection symmetries, and then explore their various consequences on model building and neutrino phenomenology. We pay particular attention to soft mu-tau symmetry breaking, which is crucial for our deeper understanding of the fine effects of flavor mixing and CP violation. |

Leptonic Unitarity Triangles and Effective Mass Triangles of the Majorana Neutrinos

Zhi-zhong Xing; Jing-yu ZhuSubjects: Physics >> Nuclear Physics

Given the best-fit results of six neutrino oscillation parameters, we plot the Dirac and Majorana unitarity triangles (UTs) of the 3\times 3 lepton flavor mixing matrix to show their real shapes for the first time. The connections of the Majorana UTs with neutrino-antineutrino oscillations and neutrino decays are explored, and the possibilities of right or isosceles UTs are discussed. In the neutrino mass limit of m_1 \to 0 or m_3 \to 0, which is allowed by current experimental data, we show how the six triangles formed by the effective Majorana neutrino masses \langle m\rangle_{\alpha\beta} (for \alpha, \beta = e, \mu, \tau) and their corresponding component vectors look like in the complex plane. The relations of such triangles to the Majorana phases and to the lepton-number-violating decays H^{++} \to \alpha^+ \beta^+ in the type-II seesaw mechanism are also illustrated. |

Neutrino Masses and Flavor Oscillations

Yifang Wang; Zhi-zhong XingSubjects: Physics >> Nuclear Physics

This essay is intended to provide a brief description of the peculiar properties of neutrinos within and beyond the standard theory of weak interactions. The focus is on the flavor oscillations of massive neutrinos, from which one has achieved some striking knowledge about their mass spectrum and flavor mixing pattern. The experimental prospects towards probing the absolute neutrino mass scale, possible Majorana nature and CP-violating effects will also be addressed. |

How to interpret a discovery or null result of the $0\nu 2\beta$ decay

Zhi-zhong Xing; Zhen-hua Zhaoy; Ye-Ling ZhouSubjects: Physics >> Nuclear Physics

The Majorana nature of massive neutrinos will be crucially probed in the next-generation experiments of the neutrinoless double-beta (0ν2β) decay. The effective mass term of this process,??m?ee, may be contaminated by new physics. So how to interpret a discovery or null result of the?0ν2β?decay in the foreseeable future is highly nontrivial. In this paper we introduce a novel three-dimensional description of?|?m?ee|, which allows us to see its sensitivity to the lightest neutrino mass and two Majorana phases in a transparent way. We take a look at to what extent the free parameters of?|?m?ee|?can be well constrained provided a signal of the?0ν2β?decay is observed someday. To fully explore lepton number violation, all the six effective Majorana mass terms??m?αβ?(for?α,β=e,μ,τ) are calculated and their lower bounds are illustrated with the two-dimensional contour figures. The effect of possible new physics on the?0ν2β?decay is also discussed in a model-independent way. We find that the result of?|?m?ee|?in the normal (or inverted) neutrino mass ordering case modified by the new physics effect may somewhat mimic that in the inverted (or normal) mass ordering case in the standard three-flavor scheme. Hence a proper interpretation of a discovery or null result of the?0ν2β?decay may demand extra information from some other measurements. |

On the four-zero texture of quark mass matrices and its stability

Zhi-zhong Xing; Zhen-hua ZhaoSubjects: Physics >> Nuclear Physics

We carry out a new study of quark mass matricesMu(up-type) and Md(down-type) which are Hermitian and have four zero entries, and find a new part of the parameter space which was missed in the previous works. We identify two more specific four-zero patterns ofMu and Md with fewer free parameters, and present two toy flavor-symmetry models which can help realize such special and interesting quark flavor structures. We also show that the texture zeros of Mu and Md are essentially stable against the evolution of energy scales in an analytical way by using the one-loop renormalization-group equations. |

Subjects: Physics >> Nuclear Physics

We have carefully examined, in both analytical and numerical ways, how small the terrestrial matter effects can be in a given medium-baseline reactor antineutrino oscillation experiment like JUNO or RENO-50. Taking the ongoing JUNO experiment for example, we show that the inclusion of terrestrial matter effects may reduce the sensitivity of the neutrino mass ordering measurement by \Delta \chi^2_{\rm MO} \simeq 0.6, and a neglect of such effects may shift the best-fit values of the flavor mixing angle \theta_{12} and the neutrino mass-squared difference \Delta_{21} by about 1\sigma to 2\sigma in the future data analysis. In addition, a preliminary estimate indicates that a 2\sigma sensitivity of establishing the terrestrial matter effects can be achieved for about 10 years of data taking at JUNO with the help of a proper near detector implementation. |

Subjects: Physics >> Nuclear Physics

Given an accelerator-based neutrino experiment with the beam energy E \lesssim 1 GeV, we expand the probabilities of \nu_\mu \to \nu_e and \overline {\nu}_\mu \to \overline {\nu}_e oscillations in matter in terms of two small quantities \Delta_{21}/\Delta_{31} and A/\Delta_{31}, where \Delta_{21} \equiv m^2_2 - m^2_1 and \Delta_{31} \equiv m^2_3 - m^2_1 are the neutrino mass-squared differences, and A measures the strength of terrestrial matter effects. Our analytical approximations are numerically more accurate than those made by Freund in this energy region, and thus they are particularly applicable for the study of leptonic CP violation in the low-energy MOMENT, ESS\nuSM and T2K oscillation experiments. As a by-product, the new analytical approximations help us to easily understand why the matter-corrected Jarlskog parameter \widetilde{\cal J} peaks at the resonance energy E_* \simeq 0.14 GeV (or 0.12 GeV) for the normal (or inverted) neutrino mass hierarchy, and how the three Dirac unitarity triangles are deformed due to the terrestrial matter contamination. We also affirm that a medium-baseline neutrino oscillation experiment with the beam energy E lying in the E_* \lesssim E \lesssim 2 E_* range is capable of exploring leptonic CP violation with little matter-induced suppression. |

[1 Pages/ 8 Totals]